Fortress Biotech, Inc. Quarterly report [Sections 13 or 15(d)]

Revenues from Contracts and Significant Customers (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025 USD ($) customer	Sep. 30, 2024 customer	Sep. 30, 2025 USD ($) customer	Sep. 30, 2024 customer	Dec. 31, 2024 customer
Revenues from Contracts and Significant Customers
Other revenue	$ 606		$ 2,010
Cutia Agreement \| Related Party \| Avenue
Revenues from Contracts and Significant Customers
Other revenue	$ 600		600
AnnJi license termination and program transfer \| Related Party \| Avenue
Revenues from Contracts and Significant Customers
Other revenue			$ 1,400
Dermatology Products Sales \| Customer Concentration Risk \| Revenue
Revenues from Contracts and Significant Customers
Number of customers \| customer	0	0	0	0
Dermatology Products Sales \| Credit Concentration Risk \| Accounts Receivable
Revenues from Contracts and Significant Customers
Number of customers \| customer			0		1
Dermatology Products Sales \| Customer One \| Credit Concentration Risk \| Accounts Receivable
Revenues from Contracts and Significant Customers
Concentration risk, percentage					10.30%